An electronic control device, such as an engine control unit or an automatic transmission control unit, which is mounted under a condition where the unit is directly splashed with liquid such as water, for example, mounted in an engine room, is configured to have a circuit board mounted with electronic parts housed in a protective space (waterproofed space) in a case made up of a plurality of case parts joined. In such an electronic control device, completely sealing a case causes stress to be applied to a harness connected to a connector portion and a waterproof portion at the tip of the harness due to a pressure difference between the inside of the case and the outside air, resulting in making liquid such as water be liable to be drawn into the unit. Therefore, a structure has been provided in which a breathing path is provided at a part of a case member and a breathing filter film having permeability and waterproofness is attached to an end surface of the breathing path (e.g. PTL 1).